Interferon-␣ and Interferon-␥ Sensitize Human Tenon Fibroblasts to Mitomycin-C

PURPOSE. To investigate the effect of interferon (IFN)-␣ and IFN-␥ pretreatment on mitomycin C (MMC)-induced cell death in human Tenon fibroblasts (HTFs) and the mechanisms by which IFN-␣ and IFN-␥ modulate the susceptibility of HTFs to MMC. METHODS. HTFs were pretreated with IFN-␣ and IFN-␥ for 48 hours before 5-minute application of 0.4 mg/mL MMC. Cell death after 48 hours was determined by Annexin V/propidium iodide (PI) staining and lactate dehydrogenase (LDH) release assay. Fas, Fas-ligand, and Bcl-2 expression were determined by flow cytometry. Fas associated death domain (FADD), Bax, cytochrome c, and caspase expression were determined by Western blot analysis and immunofluorescence staining. RESULTS. MMC treatment increased cell death and upregulated Fas and FADD expression, but had no effect on Fas-Ligand, Bax, Bcl-2, or cytochrome c. Neither IFN-␣ nor IFN-␥ alone induced HTF death, but each increased cell death 2 days after MMC treatment in a dose-dependent fashion. Combination IFN-␣ and IFN-␥ had a synergistic effect. IFN-␣ and IFN-␥ pretreatment increased Fas expression. Fas upregulation was associated with increased sensitivity to MMC. IFN pretreatment increased procaspase-8, procaspase-9, and procaspase-3 expression, and caspase-3 activation. Caspase-8, caspase-3, and broad caspase inhibitors, but not caspase-9 inhibitor, inhibited MMC-induced cell death in nonpretreated and IFN-pretreated cells. CONCLUSIONS. IFN-␣ and IFN-␥ enhance the susceptibility of HTFs to MMC-induced cell death through a Fas-mediated and a caspase-3-dependent pathway. Pretreatment with IFN primed HTFs to MMC, providing a potential means for initially slowing the healing response with IFN and subsequently terminating fibroblast activity through MMC-induced cell death. (Invest Ophthalmol Vis Sci